Biofilms caused by various kinds microbiological contamination occur frequently in the conveying system of food processing plants, hospital devices such as urinary catheters, airplane fuel tanks and pipeline filters, waste water discharge lines of nuclear power plant heat exchanger s and so on. Such biofilms not only cause the affected pipelines to narrow, reducing their capacity and wasting energy but also could contribute to corrosion of the pipelines and endanger the entire system. In food processing plants, biofilms in conveying systems could additionally cause serious quality control problems. In hospitals, contaminated equipments and devices could infect patients. In aviation, once biofilms are developed in fuel lines, they could cause deterioration in the quality of the fuel and/or seriously affect air safety by damaging the integrity of the fuel lines by pitting the wall surface of the fuel lines so covered. Needless to say, how to combat the problems caused by biofilms is a very important and pressing problem.
At the present time, methods to control biofilm development consist of proper selection of materials for the various fluid conveying systems and the addition of biocides in the systems. Such biocides as the commercially available kathon, quaternary and glutaraldehyde are used in industrial plants; and such antibiotics as tobramycin, oxytetracycline, nystatin and erythromycin are used in hospitals. The effectiveness of these various biocides are expressed in terms of MIC-minimal inhibitory concentration. However, MIC is measured against microbiological concentrations in planktonic state only, and is quite irrelevant against microbes that have become sessile. It is not unusual to use biocides in concentrations of several hundred, even thousand times the, MIC to deal with sessile microbiological contamination. The main reason for this is that once biofilms are developed, they tend to act as barriers against the biocide. The thicker the biofilm, the stronger the barrier. Indeed, many research results have already indicated that the use of MIC values to indicate biocide effectiveness is misleading, because the MIC values can not represent the actual effect of biocides on microbiologicals that have developed biofilm.
In order to truly evaluate the effectiveness of a biocide against both planktonic and sessile microbes, a way must be developed to create biofilms of different thicknesses in the laboratory. At the present time, many different systems of biofilm reactors are being tested in the laboratories. These systems consists mainly of a reactor, a reactor feed, a pump and a set of lines. However, the systems are complicated, costly, and they are energy and time consuming to operate. They take up a lot of labortatory space. Furthermore, too many variables such as the shape and size of the reactor, the flow rate of the fluid, the speed of the pump and the fluid shear stress and reflux stress created against the inner wall of the fluid lines conspire to make the thickness of the developed biofilm inconsistent and unpredictable.